In a signal processing system, in order to improve the SNR (signal to noise ratio) of a signal, it is necessary to process signals by a high-pass filter or a low-pass filter to remove some interfering signals. Referring to FIG. 1, due to a pacemaker and other reasons, in addition to normal detecting signals (which are not shown in FIG. 1) and interfering signals (which are not shown in FIG. 1), collected original signals may include mutation signals 120. Since the mutation signals 120 could be used to represent the pace-making regularity of the pacemaker, so it is necessary to reserve the mutation signals 120 during signal processing. However, when filtering the interfering signals by the high-pass filter or the low-pass filter, due to the existence of the mutation signals 120, it will inevitably lead to a distortion of the normal detecting signals and the mutation signals 120, thereby affecting the effect of signal processing.